Connector cartridge stack for electrical transmission

ABSTRACT

Connector assemblies for use with implantable medical devices having easy to assemble contacts are disclosed. The connector assemblies are generally formed by coupling a plurality of ring contacts, sealing rings, and spring contact elements together with at least one holding ring to form a connector having a common bore for receiving a medical lead cable. Contact grooves or spring chambers for positioning the spring contact elements are formed in part by assembling multiple components together. A further aspect is a provision for encasing each connector assembly or stack inside a thermoset layer or a thermoplastic layer before over-molding the same to a sealed housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending application Ser. No.12/421,874, filed Apr. 10, 2009, which is an ordinary utilityapplication of provisional application Ser. No. 61/044,408, filed Apr.11, 2008, the contents of each of which are expressly incorporatedherein by reference for all purposes.

A connector assembly for electrical transmission between a housing and apin is generally discussed herein with particular discussions directedto connector assemblies for use with implantable medical devices andconnector assemblies having an encapsulated layer made of a dielectricmaterial surrounding a stack of conductive rings and insulativeelements.

BACKGROUND

Implantable medical devices for providing electrical stimulation to bodytissues, for monitoring physiologic conditions, and for providingalternative treatments to drugs are well known in the art. Exemplaryimplantable medical devices include implantable cardio defibrillators,pacemakers, and programmable neurostimulator pulse generators, which arecollectively herein referred to as “implantable medical devices” orIMDs. These IMDs typically incorporate a hermetically sealed deviceenclosing a power source and electronic circuitry. Connected to thesealed housing, also known as a “can,” is a header assembly. The headerassembly includes electrical contact elements that are electricallycoupled to the electronic circuits or to the power source located insidethe can via conductive terminals. The header assembly provides a meansfor electrically communicating via an external medical lead cable withthe electronic circuits or power source located inside the device to theactual stimulation point.

Industry wide standards have been adopted for, among other things, thedimensions, size, pin spacing, diameter, etc. for the receptacle and themedical lead cable. Furthermore, good electrical contact must bemaintained during the life of the implantable medical device, and themedical lead cable for use with the IMD must not disconnect from thereceptacle located in the header, yet be detachable for implanting andprogramming purposes and for replacing the IMD when necessary.

Although prior art connector contacts provide viable options for medicaldevice manufacturers, the overall dimensions of existing receptaclespose manufacturing challenges. Among other things, the challenges ofplacing stackable rings in between electrically insulating seals,positioning conductive contact elements in between conductive groovesfor forming a multi-circuit receptacle, and integrating the contactassembly into the IMD are difficult, costly and time consuming.Accordingly, there is a need for a multi-circuit or multiple contactlead receptacle that not only meets the challenges associated withimplantable applications but is also easier to manufacture than avariety of existing receptacles. There is also a need for a receptaclethat is easily adaptable with existing implantable medical devices thatare easier to manufacture than a variety of existing implantable medicaldevices.

SUMMARY

Aspects of the present invention include a free standing, axiallycompressed, connector stack comprising: a plurality of conducting ringelements each having an internal diameter; a plurality of seal elementseach comprising an internal diameter; and wherein a conducting ringelement is positioned in between two adjacent seal elements; a pluralityof canted coil springs each in contact with a corresponding one of theplurality of conducting ring elements; and wherein an encapsulationlayer surrounds, at least in part, the stack and two axial ends of theencapsulation layer each overlaps a corresponding one of the pluralityof seal elements to maintain the stack axially compressed.

A further aspect of the present invention includes a method for making afree standing axially compressed connector stack comprising a pluralityof springs, a plurality of ring contact elements, and a plurality ofseal elements having a common bore, tensioning a shaft to axiallycompress the stack, and applying an encapsulating layer over, at leastin part, the stack.

In certain embodiment, the encapsulating layer is made from a dielectricmaterial.

In certain embodiment, the encapsulation layer is a thermoset polymerlayer.

Depending on the desired manufacturing needs, the thermoset polymerlayer may be applied to the stack by at least one of dipping, spraying,casting, and painting.

In other embodiments, the encapsulation layer is a thermoplastic polymersleeve. In still others, the encapsulation layer is a machined polymersleeve with an enclosure cap.

Aspects of the present also include a method for compressing animplantable medical connector stack comprising: using a temporary rod toattach to an end seal and a compression nut or similar device forputting the shaft in tension to axially compress the stack; andmaintaining the stack axially compressed after removing the temporaryrod from the end seal.

In a yet further aspect of the present invention, a method forassembling a connector comprising: providing an axially compressedstack, said compressed stack comprising an encapsulation layer; placingthe compressed stack into a header; and over-molding the header with animplantable thermoplastic or elastomer material to a sealed implantablemedical housing.

Other aspects and variations of the connector assemblies summarizedabove are also contemplated and will be more fully understood whenconsidered with respect to the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a connector stackusable with an implantable medical housing or device. The stack includesan encapsulation layer of dielectric material surrounding, at least inpart, the stack.

FIG. 2 is a cut-away perspective view of an connector stack usable withan implantable medical housing or device provided in accordance withalternative aspect of the present invention.

FIG. 3 is a schematic system view of a heated mold system forthermoforming a sleeve over a connector stack.

FIGS. 4-6 show an alternative connector stack in different stages ofassembly inside an encapsulation layer.

FIG. 7 is an exemplary implantable medical connector incorporating aconnector stack in accordance with aspects of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently preferredembodiments of connector assemblies for electrically communicating withpins for medical leads. The connector assemblies provided in accordancewith aspects of the present invention are not intended to represent theonly forms in which the present invention may be constructed orutilized. The description sets forth the features and the steps forconstructing and using the connector assemblies of the present inventionin connection with the illustrated embodiments. It is to be understoodthat the same or equivalent functions and structures may be accomplishedby different embodiments and are also intended to be encompassed withinthe spirit and scope of the present invention, especially thoseincorporating a combination of features shown in the differentembodiments included herein. As denoted elsewhere herein, like elementnumbers are intended to indicate like or similar elements or features.

Aspects of the present invention comprise the formation of connectorstacks, as shown in FIGS. 1-19 of co-pending provisional application No.61/024,660, filed Jan. 30, 2008, entitled In-Line Connectors, and toapplication Ser. No. 12/062,895, filed Apr. 4, 2008, entitled CONNECTORASSEMBLY FOR USE WITH MEDICAL DEVICES, the contents of each of which areexpressly incorporated herein by reference. In one embodiment, theassembled connector assemblies or stacks are each then placed into amold cavity and over-molded with an implantable grade polymer orelastomer, such as silicone. The individual connector assembly can alsobe inserted into a pre-molded header, which resembles a housing having acavity for receiving the connector assembly and one or more openings forplacing the connector assembly into the pre-molded header. The one ormore openings are then backfilled or sealed, typically after attachingor welding the conductors from the sealed housing to the contact rings,to complete the assembly.

The encased connector may be referred to as a connector header, forplacing on a can or sealed housing of an IMD. In one exemplaryembodiment, windows (not shown) are left exposed through the over-moldedlayer adjacent each contact ring. When the header is placed over thecan, a plurality of contact conductors in communication with a powersource and/or electronic circuits inside the can project upwardly intophysical contact with the contact rings. The contact conductors may thenwelded to a corresponding contact ring to ensure good electrical contactthrough the windows. The windows are then backfilled and sealed usingcurable implantable elastomer or polymer.

In one embodiment, an assembled connector stack is first encapsulatedwith a thermoset polymer layer or a thermoplastic polymer layer havingdielectric properties before it is welded to a plurality of leadconductors and then over-molded in a header to a sealed housing.Referring now to FIG. 1, an assembled connector stack 10 is shown havinga removable shaft or installation rod 12 temporarily positioned in thecommon bore of the stack. The connector stack 10 can embody any of theconnector stacks described in the '660 application or the '895application, and more broadly any connector stack that includes at leastone end seal 14, a plurality of conductive elements 16, a plurality ofseal elements 18, a plurality of spring contact elements 20 forproviding spring forces between a lead cable (not shown but resemblesthe removable shaft 12) and the plurality of conductive elements, and acommon bore 22 that extends between or through the various components.In one embodiment, a second end seal 24 is placed on the end of thestack, at the end opposite the first end seal 14. The second end seal 24together with the first end seal may be used to compress the alternatingstack of conductive elements 16 and seal elements 18, as furtherdiscussed below. In a preferred embodiment, the spring contact elements20 are radial canted coil springs.

In one embodiment, the connector stack 10 is assembled by mounting thevarious components 14, 16, 18, 20, 24 onto the removable shaft 12 andplacing them in mechanical contact with one another as shown in FIG. 1,and as discussed in the '660 application and the '895 application. Thenumber of conductive elements 16, seal elements 18, and spring contactelements 20 used is dependent on the number of electrically conductingnodes or leads a particular application requires, which can vary withoutdeviating from the spirit and scope of the present invention. In theembodiment shown, the stack has four conductive elements 16 and fourspring contact elements 20 for use with a four node lead cable (notshown). Again, any number from one to three or greater than four may bepracticed without deviating from the spirit and scope of the presentinvention. Similarly, two or more parallel stacks may be incorporatedonto a single can without deviating from the spirit and scope of thepresent invention.

A set screw (not shown) located on the first end seal 14 is thentightened to secure the first end of the shaft 12 to the end seal 14. Acompression nut or similar device 28 is then placed onto the shaft 12,at the shaft's second end 30, and threaded to the threaded section 32 ofthe shaft to compress the stack 10. In one embodiment, the compressionnut 28 is hand tightened. In other embodiments, a set torque amount isused and the nut 28 may be tightened to a designed axial compression byusing a marker located on the shaft or by providing a physical stop todelimit further rotation of the nut.

The assembled stack 10 may now be assembled to a header and thenattached to a can or sealed electronic housing of an implantable medicaldevice (IMD), such as an implantable pulse generator (IPG). However, ina preferred embodiment the stack 10 is first encapsulated with athermoset polymer coating before assembly to a header. In oneembodiment, the compressed stack 10 is coated with a thin film ofsealing material, either by spraying, brushing, or dipping the stackinto a thermoset polymer bath and then allowing it to cure, with orwithout heating. In one embodiment, the thermoset polymer may be epoxybut other implantable grade resins can be used. In other embodiments,the stack is encapsulated with a thermoplastic material, which isthermoformed over the stack, as further discussed below. Thus, aspectsof the present invention is understood to include an assembled stack ofalternating conductive elements and seal elements that is covered with athermoset polymer layer; wherein said thermoset polymer layer isconfigured to maintain the stack of alternating conductive elements andseal elements in a compressed state between two end seals. In aparticular embodiment, when axial compression induced by a mechanicalmeans, such as a tension nut, is removed, the thermoset polymer layer isconfigured to provide an axial compressive force between the two endseals that is greater than compared to an axial compressive forcebetween two end seals without the thermoset polymer layer and without acompression induced mechanical means.

In certain embodiments, a dielectric sleeve 36 is placed over thecompressed stack 10 before the same is encapsulated, which isschematically shown in cross-section as two parallel lines. When used,the sleeve 36 is preferably a mesh material, such as non-woven plasticfibers, having pluralities of holes or openings to facilitate bondingand reinforcement of the encapsulated layer 34. As used herein,encapsulation layer or encapsulated layer means a layer that surrounds aconnector stack, which comprises a plurality of seal elements, ringcontact elements, and spring contact elements, to maintain the stack asa stack unit. The encapsulation layer is understood to differ from aheader assembly or unit made from a separate implantable thermoplasticor elastomer material. As further discussed below, the encapsulationlayer captures a connector stack and the combination encapsulation layerand connector stack are configured to be placed into a header.

The encapsulated stack 10 may be further processed before installing thesame into a header of an IMD by preparing cutouts on the encapsulation34 for accessing the set screw and the ring contact elements. In oneembodiment, a cutout is formed around a set screw (not shown) located onthe first end seal 14 to allow access to the set screw for tighteningaround a pin or rod. In other embodiments, a set screw may be located onthe second end seal 24, which will require a corresponding cutoutadjustment for accessing the set screw. Additional cutouts are formedone over each of the contact ring elements 16 for welding the ringelements to contact leads 13 (FIG. 2) emanating from the sealed IMDhousing, as further discussed below. In another embodiment, a cutout 27is formed adjacent a compression nut or other similar device 28 forremoving or separating the nut from the portion of the encapsulation 34near the second end seal 24. Once the various cutouts or openings areformed and the set screw backed away from the shaft 12, the shaft can bewithdrawn from the common bore 22. In an alternative embodiment, theopenings on the encapsulation at the contact ring elements 16 may bemade after the shaft is withdrawn from the stack. The openings orcutouts may be made by machining, punching, laser cutting, or water-jetcutting, to name a few.

In compressing the stack 10 before applying an encapsulation layer 34around it, gaps, slacks, or looseness between the various components aretaken up. This process minimizes and possibly eliminates any chances ofpolymer seeping in between the components during the headerencapsulating process and/or during the header over-molding process inwhich the stack is incorporated into a header with an implantable gradepolymer or elastomer. Thus, another aspect of the present invention isthe provision for inspecting the stack for penetration of elastomer orpolymer materials after the encapsulation process. In one embodiment,inspection is performed by placing the stack under a magnifying glassand looking through the common bore for signs of elastomer and polymermaterials.

A method is also herein provided for making a free standing compressedconnector stack 10 comprising a plurality of springs 20, ring contactelements 16, and seal elements 18 with an accessible common bore. Freestanding is meant to connote not being bounded or confined to astationary source, such as a stationary clamp. For example, once a stackis assembled, an encapsulated layer is cured over the stack, and acompression nut and assembly rod removed from the stack, the stack is acompressed free standing stack without any compression induced devices.In another embodiment, a method for compressing a stack is providedusing a temporary rod attached to an end seal and a compression nut forputting the shaft in tension, which then axially compresses the stack.The compressed stack is capable of remaining compressed once anencapsulated layer is cured thereover and the temporary rod andcompression nut removed. In another embodiment, the free standing stackis provided in an assembled compressed state and can simply drop into aheader for over-molding to a sealed IMD housing.

In yet another embodiment, an implantable medical stack comprising acommon bore is provided in which a conductive ring contact element isaxially compressed against two adjacent non-conductive seal elements andthe compression is held by an encapsulation layer. A further aspect ofthe present invention is a method for making an implantable medicalstack comprising a common bore in which a conductive ring contactelement is axially compressed against two adjacent non-conductive sealelements, the method comprising applying an encapsulation layer aroundthe stack and curing the layer, which can be a thermoset or athermoplastic polymer, as further discussed below. Another methodprovided herein comprises the steps of making an implantable medicalstack comprising a common bore, a conductive ring contact elementaxially compressed against two adjacent non-conductive seal elements andthe compression is held by an encapsulation layer, wherein a ring groovefor retaining a canted coil spring is formed by placing at least onenon-conductive seal element adjacent a conductive ring element to createat least one side wall made from a non-conductive material. In yetanother embodiment, a method for making an implantable medical stackcomprising a common bore in which a non-conductive seal element isaxially compressed against two adjacent conductive elements, the methodcomprising applying an encapsulation layer around the stack and curingthe layer, which can be a thermoset or a thermoplastic polymer.

Another method of the present invention is a provision for creating aplurality of retaining bores in a medical connector stack foraccommodating a plurality of canted coil springs, each of said borescomprising a conductive bottom wall and at least one side wall made froma non-conducting material, and wherein said stack is held in acompressed state by a cured polymer layer, which can be a thermoset or athermoplastic polymer, as further discussed below. More broadly, amethod is provided for maintaining a stack of assembled components byfirst placing the stack in compression using a temporary shaft, applyinga polymer layer to the stack, curing, hardening, or re-hardening thepolymer layer, and removing the temporary shaft to provide an accessopening for a common bore.

Referring now to FIG. 2, a partial perspective cut-away view of anencapsulated implantable medical stack 38 provided in accordance withalternative aspects of the present invention is shown. In the presentembodiment, the medical stack 38 can embody any of the stacks disclosedin the '660 application or '895 application, which were previouslyincorporated by reference. The stack 38 can also have any number of ringcontact elements 16, seal elements 18, and canted coil springs 20depending on the particular application, with only three contactelements 16 and three canted coil springs 20 shown for mating connectionwith a three-node lead cable.

In the present embodiment, a thermoplastic sleeve 40, which is slightlylonger than the length of the stack measured from the two end-most sealelements 18, is placed over part of the stack 38 so that the two ends ofthe sleeve overhangs the two end-most seal elements 18. The nut 50 isthen tightened to a desired compression to axially compress the stack38, such as by turning the set screw 46 against the groove on the shaft48. The thermoplastic sleeve 40 may subsequently be heated to near itsglass transition temperature and allowed to cool so that the twofolded-over ends maintain the stack in the compressed state even afterthe removable shaft 48 is removed. In a particular embodiment, thethermoplastic sleeve 40 is generally cylindrical in configuration. Inanother embodiment, after the nut 50 is removed, a second end seal (notshown) is optionally positioned and secured to the stack.

In one embodiment, the sleeve 40 is preferably made from a polysulfonethermoplastic material. However, other thermoplastic polymers may beused, such as heat shrinkable fluro polymer (FEP or PEEK). In oneembodiment, the inside diameter of the sleeve is slightly larger thanthe maximum outside diameter of the stack, excluding the compressionplate 44, to provide a slip-on fit when slid over the stack 38.Depending the polymers used to make the sleeve, the thickness of thesleeve can vary. Preferably, it is sufficiently thick to resist axialexpansion of the stack after the removable shaft 48 is removed. Forpolysulfone material, it has been found that a thickness of about 20-30mils is adequate to maintain the stack in a compressed state. Heatshrinkable materials can also be used to encapsulate the stack. The heatshrinkable material may be slightly longer than the stack so that theheat shrink material folds over the ends of the stack to hold thedesized axial compression.

In one embodiment, the sleeve 38 is pre-cut with a plurality ofopenings. In a particular embodiment, an opening or cutout 52 having adiameter of slightly less than the width of a ring contact element 16 isincorporated and aligned with a corresponding ring contact element.Thus, in the embodiment shown, three openings 52 are provided adjacentthree ring contact elements. The openings 52 provide access to the ringcontact elements 16 so that that they may be welded to lead wires orconductors emanating from the sealed IMD housing. The stack shown 38,without the removable shaft 48, can then be attached to a header of anIMD. In one embodiment, an additional opening is provided for accessinga set screw used to secure/remove the removable shaft and for later usewith a lead cable. Other cutouts and openings may be incorporated asdesired.

Thus, aspects of the present invention include methods for forming anencapsulated medical connector stack comprising forming a stack, placingthe stack inside a thermoplastic sleeve, and folding two ends of thesleeve over two end axial surfaces of the stack and curing the sleeve.Another feature of the present invention is a method for forming a stackcomprising a spring retaining groove comprising a bottom surface definedby a conductive ring element and at least one side wall formed from anon-conducting elastomer, thermoplastic elastomer (TPE), or polymer, andwherein a sleeve comprising a wall surface having a diameter and alength is placed over the stack to form an encapsulation over the stack.

FIG. 3 is a schematic diagram of a heat forming system 60 forthermoforming a sleeve 62 over a compressed implantable medicalconnector stack 64 in accordance with aspects of the present invention.In one embodiment, the stack 62 can embody any of the stacks disclosedin the '660 application or '895 application, which were previouslyincorporated by reference. The stack 64 can also have any number of ringcontact elements, seal elements, and canted coil springs depending onthe particular application. For purposes of describing the equipment 60of FIG. 3, the present stack is assumed to be the same as the stack 10shown in FIG. 1.

In one embodiment, a forming dye 66 comprising an upper housing section68 and a lower housing section 70 made of a metal material is used. Thetwo housing sections 68, 70 incorporate a plurality of bores 72 forreceiving a plurality of electrical resistance heater rods, which areconnected to cables that are in turn attached to an induction heatercontroller 74. One or both housing sections 68, 70 also incorporate abore 76 for positioning a thermocouple.

Both housing sections 68, 70 incorporate a cavity 78 that together forma tight fitting space for receiving the stack 64. In a particularembodiment, the cavity 78 is sized to form a snug fit around the stack64. Thus, as the sleeve 62 is slightly longer than the length of thestack, as previously discussed with reference to FIG. 2, the sleeve isforced to fold over by the two ends 80 of the cavity 78 when thecombination sleeve and stack is placed in the cavity. When the upperhousing section 68 is placed over the lower housing section 70 with thecombination sleeve and stack positioned therein, the two ends 80 of theupper cavity 78 also force the sleeve to fold over at its two ends 82.Alignment means may also be incorporated in the heater housing to alignthe two housing sections when they mate.

The sleeve 62 can now be heated to or near its glass transitiontemperature and allowed to cool to maintain the stack in a compressedstate, as previously discussed. In one embodiment, this is accomplishedby energizing the electrical resistance heater rods to heat the upperand lower housing sections 68, 70. Once the two housing sections 68, 70heat to a set temperature, which is detected by the thermocouple, powerto the heater elements is terminated by the controller 74. The sleeve isthen allowed to air cool or forced air may be used to circulate air overthe two housing sections to more quickly quench the sleeve. Once cooled,the stack with the thermoformed encapsulation may be removed andassembled to a header and to an IMD housing. The addition of theencapsulation layer minimizes and possibly eliminates any chances ofpolymer seeping in between the components of the stack during theencapsulating process and/or during the over-molding process in whichthe stack is attached to a header with an implantable grade polymer orelastomer.

Thus, aspects of the present invention include a method forthermoforming a thermoplastic sleeve over an axially compressedimplantable medical connector stack having an open common bore by usinga heated mold to heat the sleeve to maintain the stack in a compressedstate once the sleeve cures. A further method comprises forming anencapsulation around an axially compressed medical connector stackwherein the stack comprises a groove defined by a conducting internalshoulder and at least one side wall comprising an elastomer or a TPEmaterial for retaining a canted coil spring.

A yet further method in accordance with aspects of the present inventionis a method for forming a stack over a removable shaft, tensioning theshaft to axially compress the stack, placing the stack inside athermoplastic sleeve, and placing the combination sleeve and stack intoa cavity of a heated mold. In still yet another aspect of the presentinvention, a method is provided for preventing polymer or elastomerseepage in between a seam of a pair of conductive ring element and sealelement of a connector stack, said method comprising the step of curinga sleeve over the connector stack, placing the connector stack and curedsleeve into a header, and back filling the header with curable polymeror elastomer.

FIG. 4 is an exploded cross-sectional side view yet another freestanding stack provided in accordance with another aspect of the presentinvention, which is generally designated 90. In the embodiment shown,the free standing stack 90 comprises an enclosure or housing 92, closurecap 94 and a connector stack 96, which comprises a plurality of sealelements 98, conductive elements 100, spring contact elements 20, andone or more end seals 102, 104. Although shown as an over-under typeseal element for forming seals between adjacent ring contact elementsfor an assembled stack 96 as described in the '895 application, thestack 96 shown is exemplary only and may embody any of the stacksdescribed elsewhere herein or in the '895 application. Also, the numberof ring contact elements and spring contact elements may vary dependingon the particular application. In the embodiment shown, there are threering contact elements for a three node application with fewer or moreelements contemplated.

In one embodiment, the housing 92 embodies an elongated tube having awall surface 106 that defines an interior cavity 108. The elongated tubemay be generally cylindrical but more preferably is of the size andshape sufficient to accommodate a connector stack 96. The housing has afirst end 110 having a through opening 112 and a second end 114, whichfunctions as an inlet for stacking the stack into the interior cavity ofthe housing. The through opening 112 is configured to accommodate a leadcable, such as a male pin carrying electrode leads, should the leadcable project therethrough. In other embodiments, the first end 110 hasa closed end so that an axial end of the lead cable is sealed orconfined within the interior cavity 108 of the enclosure. As the housing92 and enclosure cap 94 are configured to encapsulate the connectorstack 96, it may be referred to as an encapsulation layer.

In one embodiment, the enclosure 92 is a machined polymer sleevecomprising an interior wall surface 116 having a machined groove 118located closer to the second end 114 of the housing than the first end110. Exemplary polymer materials include peek, polysulfon, polyethyleneand silicone. As shown, the interior wall surface is generally squareand defines a generally cylindrical interior cavity. The stack may beinserted into the interior cavity one at a time in the order shown orinserted all at once as an assembled stack. In other embodiments, theinterior wall surface 116 has a draft angle or a taper that increasesfrom the first end 110 towards the second end 114 such that the insidediameter of the cavity at the second end is larger than the insidediameter of the cavity at the first end. The seal elements 98 are formedwith outside diameters that form an interference fit with the insidesurface 116 of the housing 92. For a tapered inside housing bore 108,assembly of the stack is facilitated as insertion of the inner mostcomponents, i.e., components closest to the first end 110, is easierwith a larger inlet provided by the tapered interior wall surface.However, the common bore 120 of the various seal elements should have aconstant inside dimension, such as a constant inside diameter defined bythe interior seal lips 122 to seal against a lead cable, such as amedical lead cable for medical implants. In one embodiment, theenclosure has a wall thickness of about 25 to about 60 mils depending onthe materials used. However, the thickness can vary provided it issufficiently thick to serve as an enclosure for a free standing stack.

With reference now to FIG. 5 in addition to FIG. 4, the stack 96 isplaced inside the interior cavity 108 of the enclosure 92 by firstpushing the end seal 102 into the cavity then follow by a seal element98, and a combination ring contact element 100 and spring contactelement 20 and so forth. The spring contact element 20 is preferablyplaced into physical contact inside the ring contact element 100 and isretained inside the groove provided by the ring contact element prior toplacing the combination into the interior cavity of the enclosure 92. Inother embodiments, the two are sequentially or serially placed insidethe enclosure one at a time. Thus, the present invention is understoodto include an enclosure 92 having a wall surface 106 and an end wall 124for accommodating a connector stack 96. A further aspect of the presentinvention is an enclosure cap 94 for capping an end of the enclosurehousing 92 after the connector stack 96 is placed therein to form a freestanding stack 90. The present invention is further understood toinclude an implantable medical device (IMD), such as an implantablepulse generator, a neurological stimulator, a pacemaker, an implantablecardioverter defibrillator, a cardiac resynchronization therapy device,a spinal cord stimulator, a deep brain stimulator, a vargus nervestimulator, an interstim neuromodulator, and a cochlear implant device,in which a header having a cavity is sized to accommodate a freestanding stack 90. Thus, the IMD is understood to include a firstenclosure for enclosing a connector stack and a second enclosure forenclosing the combination first enclosure and connector stack. Thesecond enclosure can be a pre-formed header having a cavity and anopening leading into the cavity and aligned with the common bore of theconnector stack.

With reference now to FIG. 6 in addition to FIG. 5, the last componentto be inserted into the enclosure 92 is an end seal 104. In oneembodiment, the end seal 104 has a section, such as an end wall 126,that straddles or overlaps with the machined groove 118. The end wall126 is configured to be pushed or abutted by a push end 128 on theenclosure cap 94 in the axial direction, which coincides with thelengthwise direction of the connector stack and/or of the enclosurehousing 92. In one embodiment, the push end 128 comprises a tapered tip130 for facilitating insertion of the cap into the opening of the secondend 114 of the housing 92. The push end 128 also incorporates a lip 132for snap-fit engagement with the machined groove 118. The snap-fitengagement seals the seam 138 that delineates the enclosure housing 92and the enclosure cap 94. In the embodiment shown, the gap or distancebetween the lip 132 and the axial end surface 134 of the push end 128may be controlled to provide a desired axial compression on the end seal104 and hence on the stack 96. In one embodiment, sufficient axialcompression is provided so that the first seal element 98 is axiallycompressed against the first end seal 102. In an alternative embodiment,the enclosure cap 94 is secured to the housing 92 by an external device,such as a clamp, external detents, welding, and bonding. In allembodiments, the combination housing and enclosure cap is understood toinclude an encapsulation layer comprising a seam.

In the assembled state shown in FIG. 6, the through bore 136 on theenclosure cap 94 aligns with the common bore 120 of the connector stack96, which may or may not align with the through opening 112 at the firstend 110 of the enclosure as it depends on whether an opening isincorporated or not at the first end 110. Thus, an aspect of the presentinvention is understood to include a housing comprising an end wall forretaining a first end of a connector stack and a cap 94 comprising apush end 128 and/or an end wall 140 for retaining a second end of theconnector stack to retain the stack within a cavity defined by thecombination enclosure housing and cap. In a still further aspect of thepresent invention, a connector assembly is provided comprising andencapsulation layer comprising a seam, said encapsulation layer definingan interior cavity and having a connector stack comprising a pluralityof seal elements, spring contact elements, and conductive elements. Theconnector stack preferably further includes at least one end cap locatedadjacent a seal element. Still more preferably, the end cap comprises aset screw.

With reference now to FIG. 7, an exemplary IMD 142 is shown, which inone particular embodiment is an implantable pulse generator (IPG) butcould be any implantable medical devices described above. The IMD 142comprises a sealed can 144 and a header 146 having a free standingconnector stack 148 disposed therein. The free standing connector stack148 could be any one of the stack described with reference to FIGS. 1-6above, which may also include any connector stack type described in the'660 application or the '895 application. A medical lead cable 148, onlypartially shown, is inserted into the common bore of the connectorstack, through the header opening 150.

Although limited preferred embodiments and methods for making and usingconnector assemblies provided in accordance with aspects of the presentinvention have been specifically described and illustrated, manymodifications and variations will be apparent to those skilled in theart. For example, various material changes may be used, incorporatingdifferent mechanical engagement means to attach the various componentsto one another, making use of two or more different materials orcomposites, making a sealing ring from multiple pieces rather than asingularly molded piece, etc. Moreover, the connector assembliesprovided herein may be used in conjunction with an Extension, which isused for testing implanted electrode terminals or implanted activatorunits so that programs or controls used to manipulate the implantedelectrode terminals and the like can be programmed for the IMD. Stillalternatively, the connector assembly may be used for any device thatrequires an in-line connection in which multiple conductive sources areto be relayed between a source generator and a source receiver, whetherthat device is configured for implanting or otherwise. Stillfurthermore, although thermoset and thermoplastic polymers are describedfor encapsulating a stack, other means may be used, such as a mechanicalclamp. Accordingly, it is to be understood that the connector assembliesconstructed according to principles of this invention may be embodied inother than as specifically described herein. The invention is alsodefined in the following claims.

1. A free standing in-line connector comprising: a stack having twoaxial ends, said stack comprising: at least two conductive ring elementseach having an internal diameter; a plurality of seal elements eachcomprising an internal diameter; and wherein a conductive ring elementis positioned in between two adjacent seal elements; at least two cantedcoil springs each in contact with one of the at least two conductivering elements; and wherein an encapsulation layer surrounds the stackand overlaps at least one of the two axial ends of the stack to maintainthe stack axially compressed outside of an implantable medical header.2. The free standing in-line connector of claim 1, wherein theencapsulation layer is made from a dielectric material.
 3. The freestanding in-line connector of claim 1, wherein the encapsulation layercomprises a seam.
 4. The free standing in-line connector of claim 1,further comprising an end seal located adjacent one of the sealelements.
 5. The free standing in-line connector of claim 4, wherein theend seal comprises a threaded bore and a set screw.
 6. The free standingin-line connector of claim 1, further comprising a header elementattached to a sealed housing of an implantable medical device, whereinthe stack and the encapsulation layer are positioned inside the headerelement.
 7. The free standing in-line connector of claim 3, wherein theseam delineates the encapsulation layer into an enclosure cap and anenclosure housing.
 8. The free standing in-line connector of claim 1,further comprising a forming dye comprising one or more heating elementsand a cavity; and wherein the stack and encapsulation layer arepositioned in the cavity.
 9. The free standing in-line connector ofclaim 8, further comprising a thermocouple connected to the forming dye.10. A free standing, axially compressed, connector stack comprising: aplurality of conducting ring elements each having an internal diameter;a plurality of seal elements each comprising an internal diameter; andwherein a conducting ring element is positioned in between two adjacentseal elements; a plurality of canted coil springs each in contact with acorresponding one of the plurality of conducting ring elements; andwherein an encapsulation layer surrounds, at least in part, the stackand two axial ends of the encapsulation layer each overlaps acorresponding end of the stack to maintain the stack axially compressed.11. The free standing, axially compressed, connector stack of claim 10,wherein the encapsulation layer is made from a dielectric material. 12.The free standing, axially compressed, connector stack of claim 10,wherein the encapsulation layer comprises a seam.
 13. The free standing,axially compressed, connector stack of claim 10, further comprising anend seal located adjacent a seal element.
 14. The free standing, axiallycompressed, connector stack of claim 12, wherein the end seal comprisesa threaded bore and a set screw.
 15. The free standing, axiallycompressed, connector stack of claim 10, further comprising a headerelement attached to a sealed housing of an implantable medical device,wherein said connector stack positioned inside said header element. 16.The free standing implantable, axially compressed, connector stack ofclaim 11, wherein the seam delineates the encapsulation layer into anenclosure cap and an enclosure housing.
 17. A free standing in-lineconnector comprising: a stack having two axial ends, said stackcomprising: a plurality of conductive ring elements each having aninternal diameter; a plurality of seal elements each comprising aninternal diameter; and wherein at least one conductive ring element ispositioned in between two adjacent seal elements; a plurality of springcontact elements each in abutting contact with a correspondingconductive ring element; the internal diameter of the plurality ofconductive ring elements and the internal diameter of the plurality ofseal elements defining a common bore; wherein an encapsulation layersurrounds the stack and overlaps at least one of the two axial ends ofthe stack to maintain the stack axially compressed outside of animplantable medical header.
 18. The free standing in-line connector ofclaim 17, further comprising a shaft located in the common bore.
 19. Thefree standing in-line connector of claim 17, further comprising a capmechanically engaged to an end of the encapsulation layer.
 20. The freestanding in-line connector of claim 17, further comprising a headerelement attached to a sealed housing of an implantable medical device,wherein the stack and the encapsulation layer are positioned inside theheader element.
 21. The free standing in-line connector of claim 17,further comprising a header element attached to a sealed housing of animplantable medical device, wherein the stack and the encapsulationlayer are positioned inside the header element.